Apparatus for measuring hydrogen absorption

ABSTRACT

The apparatus of the invention is designed to measure the amount of hydrogen that is absorbed by a metal structure. The apparatus is comprised of a receptacle having a wall section which is made of metal similar to the metal of the structure under observation. The receptacle is filled with a neutral or caustic solution. A cathode which may be a rod of lead oxide is inserted into the caustic solution. The wall section, also in contact with the solution, operates an anode in the caustic solution. Means are provided for measuring the electrical potential between the anode and the cathode, which potential will be a function of the amount of hydrogen absorbed through the anode into the solution.

United States Patent,

[72] Inventor Edward L. Ghormley Woodland Hills, Calif.

[2]] Appl. No. 758,538 [22] Filed Sept. 9, 1968 [45] Patented Dec. 21,1971 [73] Assignee North American Rockwell Corporation [54] APPARATUS FOR MEASURING HYDROGEN ABSORPTION 4 Claims, 2 Drawing Figs.

[52] U.S.Cl 204/195,

204/1 1 [5 1] Int. Cl G0ln 27/46 [50] Field of Search ..204/] l, 195

[56] References Cited UNITED STATES PATENTS 2,844,532 7/1958 White et al. 204/195 Pvooucr (ONOINI 2,886,497 5/l959 Butler 3,498,900 3/1970 Banksetal.

Primary Examiner-T. Jung Attorneys-William R. Lane, L. Lee Humphries and Edward Gugas ABSTRACT: The apparatus of the invention is designed to measure the amount of hydrogen that is absorbed by a metal structure. The apparatus is comprised ofa receptacle having a wall section which is made of metal similar to the metal of the structure under observation. The receptacle is filled with a neutral or caustic solution. A cathode which may be a rod of I lead oxide is inserted into the caustic solution. The wall section, also in contact with the solution, operates an anode in the caustic solution. Means are provided for measuring the electrical potential between the anode and the cathode, which potential will be a function of the amount of hydrogen absorbed through the anode into the solution.'

PATENTEDnmeu an alezsloso POWER POTENTIAL SOURCE DETECTOR FIG. 2

TO STRUCTURE POTENTIAL UNDER TEST DETECTOR FIG INVENTOR.

' EDWARD L. GHORMLEY www w ATTORNEY BACKGROUND OF THE INVENTION This invention pertains to the field of hydrogen instruments and more particularly to an instrument for detecting the amount of hydrogen absorbed by metal structures.

Steel structures which are used in an ocean environment can be protected from corrosion by creating an electric circuit in which the steel structure is the cathode and in which an inert or sacrificial element is the anode. The circuit is electrically connected so that current will flow from the anode to the cathode and prevent oxidation from occurring at the cathode. Unfortunately, this process may release hydrogen gas at the cathode which is then absorbed into the steel structure and which can cause embrittlement of the steel. Hydrogen embrittlement of the steel structure can occur whenever the metal is exposed to atomic hydrogen. Atomic hydrogen diffuses through the steel lattice with ease. Where crystalline dislocation or discontinuities occur in the metal, the hydrogen atoms accumulate and form molecular hydrogen. When low strength steel is used for construction, it is affected only slightly by hydrogen attack. However, in weld zones or where work hardening occurs, these materials are subject to severe attack. The new high-strength steels used for submarines and deep submergence vehicles and for submarine habitats suffer severe loss of strength when exposed to hydrogen. Also, in a marine environment as the ambient pressure is increased, there is an increased tendency for hydrogen to migrate into the steel lattice.

A typical marine cathodic protection system, as previously stated, consists of an anode and a steel cathode electrically connected to each other and immersed in sea water. A galvanic or impressed voltage causes current to flow between the two electrodes. The steel structure acts as a cathode in the couple which protects it from oxidation reactions, stress corrosion and corrosion fatigue. If too high a voltage is impressed on the system, hydrogen will be released at the cathode. A portion of the hydrogen that is released will diffuse into the steel. Hydrogen may be released by a galvanic system using a sacrificial anode connected directly to the structure or by a rectified direct current electrical system with a permanent anode. Sacrificial anodes, such as magnesium alloys, will set up a high voltage which is sufficient to release hydrogen. Even zinc anodes have been known to cause hydrogen cracking of high-strength steels. Where a permanent anode is used, the voltage is set by control of the regulator at the surface. With a rectified electrical system, it is particularly easy to set the voltage too high so that hydrogen will be released at the surface of the metal structure.

SUMMARY OF THE INVENTION In the preferred embodiment of the invention, a receptacle is provided for containing a nonacid solution. The receptacle, either all or part thereof, is made of an electrode material. A cathode electrically insulated from the electrode material projects into the solution. Potential detecting means is provided for detecting the potential between said electrode material and the cathode, which potential is a function of the hydrogen which passes through the electrode material.

The electrode material of the receptacle may be identical to the material used in the structure for which it is desired to determine the hydrogen absorption or hydrogen embrittlement. For example, if the structure is an underwater steel platform or piling, a portion of the receptacle wall may be formed using a thickness of the same steel used for the piling. By placing the instrument close to the structure, the instrument is subjected to the same environment as the structure, and in turn to the same hydrogen absorption rate. Also, although a neutral solution will provide an output potential, better results will be achieved if a caustic solution is used. Under some operating conditions, it may be desirable to apply a potential source across the cathode and anode to cause a standard current to flow. When hydrogen diffuses into the solution, the variation of the amount of current would then be an indication of the amount of hydrogen present in the solution.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provided an improved method and apparatus for detecting the amount of hydrogen absorbed into materials.

It is a further object of the present invention to provide a hydrogen absorption detector which is adaptable to detecting hydrogen absorption in various types of materials.

It is another object of the present invention to provide a hydrogen detector which is highly accurate, yet which utilizes a minimum number ofparts.

It is a further object of the present invention to provide a hydrogen detector which is capable of operation under extremely high-ambient pressures.

The aforementioned and other. objects of the present invention will become more apparent whentaken in conjunction with the following description and drawings, throughout which like characters indicate like parts, and which drawings form a part of this application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectioned view of the preferred embodiment of the invention; and

FIG. 2 is a perspective view illustrating the apparatus of FIG. I in a method-operating embodiment.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, in one construction of the hydrogen absorption apparatus 10, a liquid receptacle 16 is formed in the shape of a cylindrical cup from a material such as plastic which is electrically nonconductive, and which is relatively impervious to hydrogen penetration. In the embodiment shown, one end of the receptacle 16 is terminated with a flat plate 11 which is held in place by means of plastic bolts or other fasteners 25 and wherein 0" rings 23 are used between the mating surfaces to form a liquidtight seal. The plate 11 is changeable to enable the instrument to more closely simulate the material that is to be tested. For example, if a particular grade of steel is used in the structure undergoing test, a similar type of steel would be used as the plate 11. A correction factor would not be necessary if the material is of the same type. That is, the amount of hydrogen absorbed into the structure under test will be the same amount of hydrogen absorbed into the plate 11. Filling the cavity formed by the receptacle in the wall portion of the receptacle 11 is an alkaline solution 18. A cathode I2 is inserted into the solution 18 and is electrically connected to a potential detector 19 by means of a lead 14 which passes through the wall of the receptacle l6 and is insulated therefrom by means of an insulator 13. The cathode may be made from a lead oxide material that is compressed to form a rigid structure. The potential detector 19 may be, for example, a galvinometer-type instrument. An electrical lead 15 is connected to the electrode element which in this particular case is the wall plate 11. A resistance between the two electrodes 26 provides an electrical shunt circuit. An opening 21 is provided in the receptacle which leads to a bellows 20 to allow for expansion of the solution 18 under changes in ambient pressure. A gas vent 22 is utilized to fill the receptacle with fluid and to bleed off any gases which may be trapped inside the chamber.

In operation, hydrogen passes through the plate 11 and is converted into ionic hydrogen in the alkaline solution 18. The hydrogen in the solution migrates to the cathode 12, causing a current to flow between electrodes 11 and 12. The flow of current causes a potential difference across resistance 26. This potential is detected in the potential detector 19. The magnitude of the potential is proportional to the amount of hydrogen absorbed through the plate 11. Good results have been achieved by using a two normal solution of sodium hydroxide. Various concentrations of other alkaline or neutral solutions may be used to achieve varying increased or decreased sensitivity for the instrument. The thickness of the plate 11 also affects the relative sensitivity of the instrument and various thicknesses and surface areas may be used without departing from the scope of the invention.

Referring now to FIG. 2, the instrument is positioned in close proximity to a structure 30 to determine the hydrogen absorption rate of the structure. The electrode lead 15 is electrically connected to the structure 30, with the potential detector 19 located on the surface. A sacrificial anode 32 is shown electrically connected to the steel structure 30 by means of a DC potential source 33. The current which flows between the anode 32 and the steel structure 30 provides cathodic protection for the steel structure. As this current flows, hydrogen may be emitted at the surface of the cathode which in this case is both the structure 30 and electrode 11. By positioning the absorption instrument 10 in close proximity to the structure under test and by providing the instrument with a sensitized area made from the same material as the structure itself, the rate of hydrogen absorption by the structure should be substantially identical to the rate that hydrogen is absorbed by the instrument.

It has been determined by laboratory tests that the amount of hydrogen absorption increases substantially with pressure. Therefore, to accurately measure the hydrogen absorption of a steel structure which is mounted in an offshore location, it would be necessary to perform a plurality of tests at various depths along the steel structure. Construction of the instrument makes its use at depth feasible in that it can operate under any ambient pressure without being affected by the pressure.

While there has been shown what is considered to be the preferred embodiment of the present invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as may fall within the true scope of the invention.

What is claimed is:

l. A hydrogen absorption detection system comprising: a body of corrosive solution;

a metallic member to be protected from corrosion disposed within said body;

a protective anode electrically connected to said member to retard corrosion thereof;

means enclosing a nonacid solution, said means having a wall portion made of the same metal as said member, and an electrode enclosed within said means;

means for measuring a potential difference across said wall and said electrode;

said means for enclosing being completely submersed within said body and having pressure compensating means to equalize the pressure therein with the ambient; and

means for maintaining said wall portion and said member at the same potential.

2. The invention according to claim 1 wherein said nonacid solution is a caustic solution.

3. The invention according to claim 1 wherein said nonacid solution is a caustic solution and wherein said electrode material is steel.

4. The invention according to claim 3 wherein said cathode is lead oxide.

UNITED STATES PATENT OFFICE 3,629,090 December 21, 1971 Patent No. Dated Edward L. Ghormley Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet "Attorneys William R. Lane, L. Lee Humphr ies and Edward Gugas" should read Attorneys William R. Lane, L; Lee Humphries and Edward Dugas the figure shown at the bottom of the Abstract should appear as shown below:

33 \POWER POTENTIAL DETECTOR |9 SOURCE 1 ijy FORM PC4050 (wsg) uscoMM-oc 60376-P69 .5. GOVERNMENT PRINTING OFFICE Z |969 366-334Y Patent N0. 3 7g qn Dated December 21, 1971' lnven'tofls) Edward L. Ghormley P 2 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Signed and sealed this 4th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 6O376-P69 us GOVERNMENT PRINTING OFFICE: Iss9 o-aee-aaa, 

2. The invention according to claim 1 wherein said nonacid solution is a caustic solution.
 3. The invention according to claim 1 wherein said nonacid solution is a caustic solution and wherein said electrode material is steel.
 4. The invention according to claim 3 wherein said cathode is lead oxide. 